254 HISTORY OF ASTRONOMY. 



examination. He has thus been the independent discov- 

 erer of eleven comets, but unfortunately it subsequently 

 appeared that each of .these, save one, had been pre- 

 viously discovered in Europe. The comet of August 29, 

 1850, he discovered seven days in advance of the 

 European astronomers. Two other comets he discovered 

 on the same night that they were seen in Europe, viz., 

 those of June 5, 1845, and April 11, 1849. Having 

 found this species of observation too severe a trial for his 

 eyes, he has for the last three or four years given, up 

 comet-seeking altogether. 



In April, 1852, the Messrs. Bond commenced a series 

 of observations which contemplate the formation of a most 

 extensive catalogue of stars down to the eleventh magni- 

 tude. For this purpose they inserted in the focus of the 

 great equatorial a thin plate of mica, upon which were 

 ruled a large number of parallel and equidistant lines, 

 designed to measure differences of declination ; and per- 

 pendicular to these they introduced three other parallel 

 lines designed for observations of right ascension. The 

 telescope being fixed in the meridian, with the first set of 

 lines parallel to the horizon, if the times of passage of any 

 number of stars over the vertical lines be observed, we 

 shall have their differences of right ascension ; and by ob- 

 serving near which of the horizontal lines they traverse 

 the field of the telescope, we shall obtain their differences 

 of declination. The observations of right ascension are 

 all recorded by the electro-magnetic apparatus in the 

 manner already described. The method pursued, there- 



